1. Field of Invention
The invention relates to a fan and an impeller thereof, and, in particular, to a fan and an impeller thereof that can reduce noise and increase airflow quantity.
2. Related Art
Since the present electronic products are rapidly developed towards high performance, high frequency, high speed and more compact, the generated heat of the electronic products becomes greater. Utilizing a fan to dissipate the heat generated by the electronic products is a common solution. In this case, the airflow pressure and the airflow quantity of the fan are important reference factors for determining the performance of the fan. Besides, the noise of the fan is also an important reference factor for the fan.
As shown in FIG. 1, a conventional fan 1 includes an impeller 11 and a motor (not shown). The impeller 11 includes a hub 111 and a plurality of blades 112, which are connected to and disposed around the periphery of the hub 111. The periphery of the hub 111 has a ring-shaped guiding angle 1111. Herein, the guiding angle 1111 is a round angle for guiding the airflow around the hub 111 into the blades 112, so that the air intake efficiency of the fan 1 can be increased.
However, when the curvature of the guiding angle 1111 is increased, the air-inlet end of the blades 112 may form an air resistant area with a large turn, which decreases the performance of the fan 1. If the curvature of the guiding angle 1111 is decreased, the air located at the periphery of the hub 111 may not be guided into the blades 112. In addition, the air-inlet area of the blades 112 is composed of the top portions of two adjacent blades. Thus, no matter how many degrees the guiding angle 1111 is, the air-inlet area of the blades 112 remains the same, resulting in that the air intake efficiency of the fan 1 can not be increased.
As shown in FIG. 2, no matter how many degrees the ring-shaped guiding angle 1111 is, the airflow will generate the vortexes 1121 and the airflow separation phenomenon behind the blades 112 after passing through the blades 112. This will affect the performance of the fan 1 and generate the noise.
Therefore, it is an important subject of the invention to provide a fan and an impeller thereof, which can increase the actual air intake, decrease the noise when the impeller rotates, and improve the performance of the fan.